Once you have your character sitting right there in your head, all you really need to do is wind them up, put them down, and simply write down what they do, say, or think.
Terry PratchettThe landscape was snow and green ice on broken mountains. These weren't old mountains, worn down by time and weather and full of gentle ski slopes, but young, sulky, adolescent mountains. They held secret ravines and merciless crevices. One yodel out of place would attract, not the jolly echo of a lonely goatherd, but fifty tons of express-delivery snow.
Terry Pratchett